Acute heart failure is the sudden inability of the heart to fill with or pump a sufficient volume of blood. The afflicted patient may become weak and short of breath and, in some instances, die. In the most severe acute heart-failure episodes, a patient experiences cardiogenic shock, a condition that is associated with high reported mortality rates.
Acute heart failure occurs in a variety of contexts. For example, some patients who are hospitalized for Acute Coronary Syndrome (i.e., heart attack and unstable angina) develop acute heart failure. Furthermore, some open-heart surgery patients develop acute heart failure. Acute heart failure also complicates certain illnesses. Additionally, some patients who undergo a Percutaneous Coronary Intervention or other procedure are at risk for developing acute heart failure or dying.
Acute heart failure does not necessarily progress to chronic heart failure or death; recovery is possible. Many patients who have acute heart failure and those at risk for developing it receive interventions that are intended to temporarily assist the heart during a recovery period. The intervention typically lasts for less than a week, but may last longer.
These interventions may include pharmaceuticals and medical devices, including cardiac-assist devices. When these cardiac-assist devices include a pump that supplements the heart's pumping action, they often are referred to as “blood pumps.” An effective cardiac-assist device assumes some of the heart's pumping function, thereby unloading the heart and enabling it to recover. Cardiac-assist devices and blood pumps can be temporary or permanent.
Over the years, various types of temporary blood pumps have been developed. One type of temporary blood pump is the catheter blood pump. This type of blood pump has a cable-driven rotor that is attached to a catheter. The catheter is inserted into a peripheral vessel, such as the femoral artery, and is then typically advanced to the aorta.
The catheter encloses a rotating drive cable that couples to impeller blades at one end. The other end of the drive cable couples to an extracorporeal motor. As the motor turns, the drive cable rotates, thereby conveying motor torque through the length of the catheter to the impeller blades. This causes the impeller to rotate at high speed, usually in the range of about 1000 to about 100,000 rpm. The impeller's rotation induces a flow of blood through the pump.
One of the more problematic components of the catheter blood pump is the drive cable/catheter assembly. Among other issues for concern, it is very difficult to provide a drive cable/catheter assembly that:                is capable of rotating at the required speeds; and        has the flexibility to negotiate small-radii bends, such as the aortic arch, as occur in the vascular system; and        is able to maintain structural integrity for a clinically relevant duration (e.g., hours to weeks, etc.) at operating speed.        
Flexible drive cables currently exist; a common example is an automobile speedometer cable. But these cables operate at gentle curvature and low speed; they are not suitable for use at higher speeds in geometries having small-radii bends.
Rods (solid or hollow) are suitable for transmitting torque at high rpm, but only if the rod is relatively straight. A rod is too stiff to spin in an arc; it will soon fracture and fail. Failure occurs even if the rod is constructed of a super-elastic material, such as Nitinol.
Coils are better suited than solid rods for high-speed operation over small-radii bends. In fact, coils are currently available for transmitting torque “around corners” for long-length applications. But manufacturers normally limit these coils to maximum operating speeds of about 20,000 rpm. As previously mentioned, catheter blood pumps often operate at rotational speeds well in excess of 20,000 rpm. In fact, in some instances, rotational speeds of up to 100,000 rpm might be required.
To avoid the problematic nature of drive cables in catheter blood pumps, some blood pumps have been developed that have a miniature motor that is positioned adjacent to the impeller blades of the pump. In such devices, the motor is implanted in the vascular system or heart along with the pump, and therefore drives the blades directly. See, e.g., U.S. Pat. No. 6,794,789.
But an implantable motor is expensive and complicated, given the extreme miniaturization and wiring/sealing challenges associated with a motor/pump combination that is significantly smaller than the diameter of an average “BB” used in BB guns (i.e., 0.177 inches in diameter). Since these blood pumps are single-use, disposable devices, the high cost of such a miniaturized, implantable motor is particularly disadvantageous.
There is a need, therefore, for a drive cable/catheter assembly that (1) can rotate at speeds well in excess of 20,000 rpm (2) while conforming to an anatomy that includes small-radii bends (3) and can maintain structural integrity for a clinically relevant duration.